This invention relates to an expandable polymeric composition of matter and method of preparation, and more particularly to an expandable alkenyl aromatic polymer composition with a volatile blowing agent and an expansion aid.
Alkenyl aromatic polymer foams such as polystyrene foams have found a wide variety of usages including insulation, cushion packaging, and the formation of molded articles such as cups, trays, and the like. When utilized as an insulating material, especially as loose fill particles, or cushion packaging material, expansion of the polystyrene foam to very low densities is quite desirable.
Steam expansion is a widely applied technology in preparing a styrenic polymer foam. Atmospheric steam (i.e., steam at atmospheric pressure) is often used to expand polystyrene resins. Both on-line and off-line expansion techniques have been utilized. In expanding polystyrene foams, it is desirable to have rapid expansion to low densities. This reduces energy and materials costs. Also desirable is the ability to expand the foam over a range of operable temperatures rather than in only a narrow temperature range because of difficulties in maintaining optimum temperatures during the entire expansion cycle.
In the past, previous attempts have been made to utilize plasticizers and/or plasticizing blowing agents in polystyrene foams to aid in expansion, particularly where very low densities are desired. Such plasticizers improve the speed of expansion but have been found to have an adverse effect on the final foam properties, and in some instances have resulted in a permanent softening of the foam.
Cross-linking of the foam during expansion to stabilize cell formation has also been attempted. However, the use of crosslinking agents may be carefully controlled as insufficient crosslinking does not produce the desired stabilization and over crosslinking makes processing difficult. Moreover, crosslinking of such foams has been determined to make reprocessing of the foam scraps difficult.
Accordingly, the need still exists in the art for an alkenyl aromatic polymer foam, which when exposed to steam or hot air expands rapidly to very low densities. Additionally, the need exists for such a foam to be easily reprocessable to enable savings in materials costs.